In my U.S. Pat. No. 4,287,972 for AUTOMATIC CLUTCH ASSEMBLY, there is disclosed a novel and improved form of clutch which is capable of effecting positive engagement between a drive member and driven member in response to the application of torque to the drive member; and further to effect positive disengagement when torque is removed and the direction of rotation of the drive member is reversed. This is done through the cooperation of concentrically arranged cam members having aligned slots, each set of aligned slots receiving a cam follower in the form of a roller pin which is associated with a drive member; rotation of the drive member will then cause each roller pin to advance in a predetermined direction along the aligned slots and to carry the drive member into engagement with the driven member. Once the engagement position is made, one of the concentric cam members is forced away from a normally locked or fixed position while the other cam member will continue to retain the roller pins in a raised position maintaining engagement between the drive and driven members irrespective of whether torque is still applied to the driving member. It is therefore necessary to reverse the rotation of the driven member to impart a reverse movement to the cam followers within the slots and to cause the one cam member to return to its original locked position as the drive member is forced away from engagement with a driven member. This arrangement has particular advantages when applied to conversion of the two-wheel drive vehicles in and out of four-wheel drive in that the drive member can be splined to the axle for engagement with a driven member associated with the wheel hub whenever torque is applied to the axle. The wheel hub will remain engaged so long as rotation continues in a given direction notwithstanding any resistance of the driving member and drive train. Also, the drive member will continue to engage the driven member associated with the wheel hub after torque has been removed from the drive member, not-withstanding power train resistance, so long as the driven member turns the driving member in the same rotational direction.
It is an aim of the present invention to lend further novel and improved characteristics to clutch assemblies of the type described in my hereinbefore referred to patent and particularly to the end of further enhancing the safety and reliability of same under all operating conditions and to further minimize any possibility of damage to the parts under abusive operating conditions.
The novel features and characteristics of the present invention may be best exemplified by describing its use in conjunction with four-wheel drive motor vehicles of the type having a synchronized transfer case which will enable the vehicle operator to selectively engage or disengage power into a front propeller shaft so that in the four-wheel drive mode the operator will have shifted the transfer case whereby power is transmitted through the front propeller shaft to both of the front wheels as well as the power which is transmitted to the rear wheels. Typically, the front propeller shaft and differential are laterally offset to permit vertical suspension movement or thrusting in relation to the chassis during vehicle operation. As a result, there is a substantial variation in linear distance of power transmission from the transfer case into each of the front wheels as well as the rear drive axle. When shifted to the four-wheel drive mode, the front wheel located nearest to the differential and power shaft will receive a torque impulse slightly ahead of the other wheel and accordingly there is a disproportionate application of torque during vehicle start-up in the four-wheel drive mode. Disproportionate applications of torque are experienced also when the vehicle operator is required to apply forward and reverse cycling applications of torque to rock the vehicle forwards and backwards to become unstuck and which torque imbalance is aggravated greatly by varying degrees of surface adhesion of the wheels during a rock cycle.
In recent years, at least one of the vehicle manufacturers has introduced a synchronized transfer case which is a form of friction clutch for imparting torque and rotation to the front propeller shaft prior to mechanical engagement of the front propeller shaft. In other words, after the front propeller shaft is brought up to the speed of the transfer case gearing, the transfer case will then mechanically engage the front propeller shaft. Accordingly, while clutch assemblies presently in use would permit shifting to the four-wheel drive mode when the vehicle was standing still, the advent of the synchronized transfer case permits dynamic engagement; or, in other words, shifting of the vehicle from two-wheel drive to four-wheel drive while the vehicle is moving at speeds on the order of 30 mph to 50 mph. When shifted "on the fly", the transfer case will turn the propeller shaft at a relatively low rpm but with sufficient torque to actuate the clutch assemblies on the front wheels toward engagement. Thus, the vehicle wheels and driven or receiving gears in the clutch assemblies may be rotated at 400 rpm to 600 rpm when the drive gear is moving into engagement at a much lower rpm. By virtue of the receiving gear being driven at a higher rpm than the drive gear, it will prevent any penetration by the drive gear into intermeshing engagement with the driven gear until the drive gear is finally brought up to a speed closely approximating that of the receiving gear, at which point the drive gear will begin to penetrate the driven gear to an extent such that the receiving gear will act as the drive gear and begin to apply torque to the normal drive gear. It is important to recognize that until the drive gear is permitted to move into a position of intermeshing engagement with the driven gear it will be effectively locked against rotation by its actuating mechanism unless some means is provided to override the locking resistance and permit the drive gear to undergo limited rotation sufficient to become synchronized with and penetrate the rotating driven gear. Essentially, a change or increase in speed of the axle drive gear to the higher rpms necessary to match wheel speed will occur within a limited time on the order of one second or less and it is therefore highly desirable that the locking resistance to drive gear rotation be overcome and overridden for that limited time interval necessary to permit dynamic engagement between the gears.
Under the conditions described and specifically as the drive and driven gears approach the pre-engagement condition in which the ears are nearly matched in speed, there is a tendency to develop a mild ratcheting or chattering at the gear interface which in the case of conventional square-edged splined faces at the interface will tend to deform the intercepting edges so as to prevent full engagement between the gears, chipping of the edges of the gears at the interface as well as wear and abrupt engagement. It is therefore desirable to avoid danger of any damage to the interfacing gear edges while at the same time to encourage more rapid, smoother penetration of the drive gear into intermeshing relation to the driven gear particularly in the course of dynamic engagement.
Still another problem to overcome is that of compensating for the disproportionate application of torque to opposite ground-engaging wheels particularly under the aforementioned conditions. It is desirable to synchronize the actuation of the clutch assemblies both in the course of engagement and disengagement so as to compensate for disproportionate application of torque as well as to prevent generation of false torques in the two-wheel drive mode which would otherwise tend to actuate the clutch assemblies accidentally.
Other representative patents, in addition to my hereinbefore referred to U.S. Pat. No. 4,287,972 are U.S. Pat. Nos. 3,217,847 and 4,238,014 to the present applicant; M. J. Fogelberg U.S. Pat. Nos. 4,192,411, 4,281,749 and 4,300,667; F. Hegar U.S. Pat. No. 3,442,361; and R. W. Goble U.S. Pat. No. 3,656,598.